The present invention relates to a flat panel display device of the type which includes electron beam sources having electron sources (cathodes) which emit electrons in response to an electric field and a phosphor screen which is excited by electron beams emitted from the electron beam sources, and, more particularly, the invention relates to a flat panel display device which is capable of producing an image display of high definition by focusing electron beams on a phosphor screen.
Recently, a field-emission-type flat panel display device has been developed which uses diamond, carbon nanotubes or the like as the material for electron sources which emit electrons in response to a low electric field. These electron sources will be referred to as cathodes hereinafter. This type of cathode can obtain a sufficient emission of electrons in response to an extremely low electric field compared with conventional field-emission-type cathodes which use a metal material as a main material. The flat panel display device which uses such an electron emission material as a cathode is disclosed in Japanese Unexamined Patent Publication 2000-268706 (patent literature 1) and Japanese Unexamined Patent Publication 2002-25478 (patent literature 2), for example. The flat panel display device described in these publications is a kind of cathode tube in which a back panel and a face panel have respective main surfaces which face each other in an opposed manner, and the peripheries of these panels are sealed by a sealing frame and a vacuum is created in the inside of the sealed structure. Here, the back panel has a so-called in-plane-gate (hereinafter abbreviated as IPG) structure in which cathodes operating as electron beam sources and control electrodes are formed on the same plane of a main surface of a back substrate which constitutes a first substrate, while the face panel includes a phosphor screen to which phosphors are applied to a main surface of a face substrate which constitutes a second substrate.
In the flat panel display device having the electron beam sources of the IPG structure, to effectively excite the phosphors with the electron beams from the electron beam sources, it is effective to provide focusing electrodes. To provide focusing electrodes to the back substrate of IPG structure, it is necessary to provide focusing electrode lines in addition to control electrode lines which supply electricity to the control electrodes. Japanese Unexamined Patent Publication 2000-3664 (patent literature 3) discloses a flat panel display device which includes electron sources of the Spindt structure and electron beam sources formed of control electrodes, wherein focusing electrodes having a partition-wall shape which surround respective pixel regions are formed over the electron beam sources, and the focusing electrodes are connected with control electrode lines of neighboring pixels.